German authorities say a man who was taken into custody on suspicion of ties with the Islamic State group denies membership in the organization and has been released.

The 31-year-old Syrian was detained at a refugee center in the western town of Unna on Thursday. He had been accused on an Arabic-language website of having worked for IS.

Dortmund prosecutor Henner Kruse said Friday the man denied being an IS member and authorities couldn't prove that he was, news agency dpa reported.

Kruse said that "the suspicion is very vague at best" and noted that it's not unusual for people to be denounced online. The man was released later Thursday.